2012-09-13

Optimistic Pessimist

Page 495, The Engineer, 17 November, 1905. John Gavey has doubts about the reach of the telephone. And demonstrates with experiment. But he is hopeful these limitations (about 45 miles) would soon be addressed.

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THE LIMITATIONS OF THE TELEPHONE.ELECTRICAL inter-communication by telephone has become such an important factor in every-day life that it is not a matter for surprise that Mr. John Gavey, in his presidential address to the Institution of Electrical Engineers, delivered on Thursday, 9th inst., should have dealt largely with this subject. It would appear from Mr. Gavey’s remarks that for short distance messages the telephone was seriously threatening the telegraph; but, as he pointed out, the questions of cost and physical limitations of the former at present prescribed the radius of its efficient employment. The distance that speech could be transmitted through cables was limited. One of the problems for the coming electrician to solve was the increase of this distance. The reason for the restriction was to be found in the attenuation and distortion of the electrical waves or impulses in cables, which results in telephone authorities usually considering 42 to 46 miles of English standard lead-covered paper insulated cable as the limit of effective commercial speech. Not the least interesting part of Mr. Gavey’s address was his presentation of some oscillograph records showing the attenuation which takes place through one mile and through 20 miles of the standard cable. A number of letters were rapidly spoken into the transmitter, and the respective transmitted and received curves recorded in the usual photographic manner. In the one mile length the curves at opposite ends were almost counterparts of one another, the differences of amplitude were inappreciable, and all the irregularities of each transmitted curve were faithfully reproduced at the distant end. When experiments were made with the longer length of cable the difference of amplitude was strongly marked, and it became difficult to compare the shapes of the two curves, although these still bore a substantial resemblance one to the other. This line of investigation was to be carried a good deal further, and Mr. Gavey would appear to be by no means hopeless regarding the future, for The concluded his address with these words :— "I have little doubt that the progress of electrical means of inter-communication will in the future go on unchecked, and that those associated with and responsible for such progress will, in the course of the next few years, bring about such developments that they be in a position to compare in no un-unfavourable manner the advance of these particular branches of our work with that which we can foresee in all other branches."